1. Field of the Invention
This invention relates to a flash device and more particularly to a flash device having a processing circuit such as an aperture control circuit which is composed of an integrated circuit.
2. Description of the Prior Art
Flash devices generally includes some processing circuit or processor that facilitates flash photography by automatically determining either a flash quantity or an aperture value for a flash. Flash devices of this kind are known, for example, from Japanese Patent Application No. SHO 57-19043 (Japanese Patent Application Laid-Open No. SHO 58-118626,corresponding to U.S. patent application Ser. No. 444,214) and U.S. Pat. Nos. 4,047,194; 4,315,679; 4,078,242; and 4,187,019. Integrated circuits are employed for such processing circuits. Therefore, power to the processing circuit must have a highly stable voltage.
A flash action in a flash device causes a drop in the voltage of the power source. This drop is attributable to the operation of a booster circuit which begins charging flash energy in a storage capacitor after each flash. Accordingly, after a flash, the voltage of power supply to the processing circuit tends to become lower than acceptable by the integrated circuit employed as the processor.
Conceivably, this problem may be overcome by supplying power to the processing circuit bia a smoothing capacitor. However, to supply a stable voltage over a long period of time with this method, the smoothing capacitor must have a large capacitance. Such arrangement not only presents another problem with respect to power consumption but also makes it impossible to render the processing circuit inoperative immediately after a power source switch is turned off.
Meanwhile, the aforementioned U.S. patent application Ser. No. 444,214 proposes a device to solve these problems by supplying power to the processing circuit from a capacitor with a back-up electric charge.